The world's grain processing industry has always experienced losses due to spoilage of harvested grain in long-term storage. Poorly controlled moisture and temperature conditions within a grain mass foster undesirable chemical and biological breakdown of grain kernels due to mold and insect growth, leading to a chain reaction of spoilage that often spreads widely within a storage bin. The adverse economic impact of spoilage is well known. In the United States alone, total annual storage losses are estimated at more than $1 billion. Worldwide, 10 to 20 percent of the global grain harvest is lost each year to improper or inefficient storage and handling. In the words of Patricia Woertz, CEO Archer Daniels Midland Company, “Clearly, agriculture must do better. Preserving what is already grown is critical . . . Mitigating post-harvest losses is part of a four-part approach needed to ensure agriculture's ability to fulfill the world's increasing food and energy needs.” (address to World Economic Forum Annual Meeting, Davos, Switzerland, 1-27-2010).
This long-felt problem has spurred the development of technological solutions to augment or supplant human-based surveillance of grain stocks. The persistent need for a solution is evident in the proliferation of so-called temperature cable systems, which are in wide use for the purpose of monitoring stored grain temperature. A temperature cable's linear array of thermal sensors detects spoilage by detecting the heat generated by an exothermic chemical or biological spoilage event. This basic functionality has made temperature cables a well known product in the market. OPI Systems with their StorMax temperature cable product line, SafeGrain with their SafeTrack temperature monitoring system and Rolfes @Boone with their BCS 1000 temperature cable monitoring product are all companies that have benefited from the commercial success of this technology.
The elapsed time between the development of a quality problem in stored grain, detection of the problem and performance of necessary mitigation actions has always been critical to the economic viability of any grain storage, transshipment or processing operation. Non-automated labor intensive surveillance methods have traditionally been slow and unreliable, resulting in large losses due to undetected spoilage. The proliferation of temperature cable systems has led to more repeatable measurements, but it has essentially automated a relatively slow detection process. Because of the insulation properties of grain, the generation of detectable temperature changes in the grain mass may lag the growth of economically significant spoilage by days or weeks. This, in turn, has led many grain managers to continue a costly human-based quality surveillance regimen despite the presence of a temperature monitoring system.
Despite common use of temperature cable systems throughout the grain storage industry, undetected spoilage and huge losses from stored grain inventories is a common event. Even though they are considered to be an incremental improvement over exclusively human-based grain surveillance, temperature cables have a significant shortcoming. It is well known that the thermal impedance of the monitored grain inhibits the effectiveness of spoilage detection due to the need to be very close to the heat generating site. Because of the low thermal conductivity of bulk grain, a single temperature measurement must be within about 0.5 m (Sinha and Wallace, 1965) or less of an active spoilage spot to detect the self-heating. This thermal insulation, and associated proximity requirement, results in blind zones where temperature cables cannot sense grain condition. In order for a storage site operator to detect spoilage with 100% reliability, a prohibitively large number of cables would be required to ensure no portion of the bin volume was outside the thermal insulation distance.
Furthermore, because of the low thermal conductivity of grain, self-heating can lead to spontaneous combustion or smoldering which, if undetected, can result in a fire inside the grain bin, a direct threat to physical plant and personnel safety.
Grain spoilage has historically been the root cause of another unfortunate safety issue, grain engulfment accidents. Spoiled grain can cause a number of unsafe conditions inside a grain bin, including the formation of crusted grain bridges and large accumulations of grain adhered to the sidewalls of a bin. Very often, when workers enter grain bins with these conditions present, the surface crust or sidewall accumulations unexpectedly give way and workers become engulfed in an avalanche of grain. Such accidents often lead to injury or suffocation and continue to be a cause for concern among grain storage facility managers, farmers and government safety agencies such as OSHA.